The technique about accurate alignment of a plurality of beams of laser can be applied to the industrial field of sophisticated manufacture detection, and is also applicable to other specific fields in which a plurality of beams of laser are applied to be aligned to a tiny object. In these applications, a dedicated laser alignment device is used to guide several hundred of beams of laser to a target region within a range of several millimeters. Furthermore, the target is ablated by the several hundred of beams of laser. Normally, the process of aligning a plurality of beams of laser to a target is called a laser-target alignment process, and a dedicated sensor for aligning the plurality of beams of laser to the target in the laser alignment device to the target is called a laser-target alignment sensor.
Conventional laser-target alignment sensor works in a conjugate reflection condition to avoid distortion and scattering which otherwise are caused by direct radiation of laser beams. It solves the problem of aligning laser to the target to some extent, and improves accuracy of the laser-target alignment to some extent. However, when several hundred of laser beams are guided simultaneously to shoot the target, the laser-target alignment sensor has the problem that feedback spots are overlapped with each other and interferences with each other. Consequently, the laser-target alignment sensor cannot obtain accurate feedback of each incident laser beam. The problem may be solved by guiding a single laser beam each time to shoot the target, which, however, is very time-consuming. Besides, the originally-aligned laser beams may depart from the target over time, because the laser beams drift over time and physical and chemical characteristics of the system vary over time. To improve accuracy of alignment, one should take more time for adjustment. The more time for adjustment, the more serious an effect of the system drift on the accuracy is. Consequently, the compromise in the laser-target alignment is almost impossible.
That is, the conventional laser-target alignment sensor cannot achieve the compromise between accuracy and efficiency of adjustment in the laser-target alignment process.
Moreover, the conventional laser-target alignment sensor can only provide information about a position of a laser spot on a screen, but not information about a spatial location of the laser beam, such as a pitch angle of the incident laser beam. The conventional laser-target alignment sensor cannot be used to control spatial distribution of laser beams in a target chamber to optimize energy distribution of the laser beams in the target chamber.